On 1/3/2016 3:16 PM, Michael wrote:
1990 928,

Very slow cranking and battery drops to about 10.5 VDC.
Battery fully charged and tested and checks good for cranking amps off car.

At first I thought it was the module that allows the car to run on 4 cylinders, however there is no LED indication that one cylinder bank or the other is inop.
I have in the past been driving and all of a sudden the car cuts to 4 cylinders and runs very rough. I pull off tap on the module and restart the car and am on my way.

Bad starter?
Anything else to check?

Let me know
Thank you,


First, I really, really hope that the car does this when it is cold, not only when it is hot. If it is turning slowly only when the engine is warm/hot, there may be a much more serious problem, usually called thrust bearing failure.

Start by carefully cleaning the battery posts, inside of the battery terminals, all of the small connections on the positive terminal, the body end of the ground strap, and the connection area where that terminal attaches. Do not assume that because the metal "looks clean" that it is OK. Clean every contact surface to shiny bright metal.

Crank the engine for a couple of minutes, then immediately feel of every battery cable and all cable connections. Any warmth indicates a poor connection or faulty cable.

The woven flat ground strap can develop high resistance and cause this, as can the ground cable from the bottom of the engine to the chassis. One way to check is to use a GOOD, heavy jumper cable in parallel to (not in place of) the ground strap - have the clamp on one end clamped on so it connects to the top of the battery post, and the other end clamped to a good chassis ground - bare metal, with a good firm connection. If there is any difference in cranking speed, you might need a new ground strap.

It is more difficult, but it is a very good idea to also clean all connections on the ground strap from the bottom of the engine near the clutch housing to the chassis.

If you carefully and correctly do all of this and it doesn't help, then consider having the starter rebuilt. My suggestion is to find a good local "auto electrical shop" - not a general garage, not an auto parts store, but a shop that specializes in repairing and rebuilding starters, generators, alternators, etc. They can check the starter completely, and replace the bearings and brushes with no trouble. This way, you are assured that the starter is the correct one for your car...